Discussion
If an object of mass 30 kg is moving with a uniform velocity of 8 metre/second, then what is the value of kinetic energy possessed by the object?
Answer: A
Kinetic energy is half the mass times the square of the velocity.
\[ KE = \tfrac{1}{2} m v^{2} \]
\[ KE = \tfrac{1}{2} \times 30 \times 64 = 960\ \mathrm{J} \]
So the object has 960 J of kinetic energy, option (A). The value 120 J comes from using the velocity without squaring it (15 x 8), and 480 J and 240 J come from mistakes in squaring or halving, so they are wrong. The kinetic energy therefore depends on the square of the speed, so doubling the speed of this object to 16 metres per second would increase its energy fourfold, to 3840 J.
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